Method and apparatus for measuring liquid quantity in bulk containers

ABSTRACT

A method and apparatus for measuring the mass of liquid within collapsible, bulk fabric storage containers is provided wherein a deflection member arranged in a grid pattern supports the container and undergoes deflection creating an increase in the pressure of fluid within its interior which may be measured and correlated to the mass of the liquid within the container.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for measuring theliquid quantity in bulk containers, and, more particularly, to one ormore deflection members arranged in a grid pattern which supports thebulk container and produces a pressure measurement that may becorrelated to the mass of liquid within the container.

BACKGROUND OF THE INVENTION

On the battlefield, the armed forces rely heavily on collapsible fabricstorage containers for temporary storage of fuel and water. These bulkcontainers range in size from 3000 gallons to 210,000 gallons, andbecause they are made of fabric such containers assume different sizeand shape depending on the amount of liquid in their interior. Bulkfabric tanks of this type pose several technical difficulties inaccounting for the volume of fuel and water used by the armed forces,due to problems in accurately measuring volume in a container ofvariable size and shape.

The current method for tracking the volume of fuel or water in bulkfabric storage containers is to measure the liquid as the container isfilled or emptied using flow meters. One limitation of flow meters isthat they are relatively inaccurate. It has been found that volumemeasurements taken on the contents of existing bulk fabric storagecontainers by flow meters may vary as much as 6% to 10%, plus or minus,compared to actual volume. This assumes that the flow meters are reseton a daily basis. If the flow meters are not reset, the accuracy is evenworse due to cumulative error.

Another issue with bulk fabric storage containers is that even ifcurrent measurement techniques were capable of accurately determiningvolume levels during filling and/or emptying, the walls of suchcontainers are semi-permeable and liquid can be lost through the wallsvia diffusion. Losses also occur through the venting system of thecontainer. Consequently, volume measurements depending on flow metersare subject to further inaccuracies as liquid is pumped in or out of thecontainer during use.

SUMMARY OF THE INVENTION

This invention is directed to a method and apparatus for measuring themass of liquid within collapsible, bulk fabric storage containerswherein a deflection member arranged in a grid pattern undergoesdeflection in response to the application of a load creating an increasein the pressure of fluid within its interior which is measured andcorrelated to the mass of the load.

In one presently preferred embodiment of this invention, the deflectionmember comprises at least one flexible line arranged in a grid patternon which a container is positioned. The flexible line(s) has a hollowinterior filled with a fluid, e.g. liquid or gas. The cross sectionalarea of the flexible line(s) decreases under the application of a load,e.g. as a container thereon is filled with liquid, and this results inan increase in the pressure of the fluid within the line(s). A pressuremeasurement device, such as a digital pressure gauge, is coupled to theline(s) and produces a measurement of the fluid pressure therein thatmay be correlated to the mass of the liquid within the container. Atemperature sensor may also be coupled to the line(s) of the gridpattern to account for the effects of temperature change of the fluid inthe line(s) on the pressure measurement.

The cross sectional area of the line(s) varies with the mass of theliquid within the container, and the pressure of the fluid within theline(s) changes accordingly. Because the container rests upon the gridpattern formed by the flexible line(s), changes in the size and shape ofthe container as it is filled and emptied do not affect the accuracy ofthe pressure measurements taken by the pressure measurement device.

The at least one flexible line noted above may comprise a singleflexible line oriented in a zig-zag or other grid pattern having adimension to accommodate the size of the container, or, alternatively, anumber of flexible lines may be arranged in a grid pattern and connectedto one another or to one or more common lines which are coupled to oneor more pressure measurement devices and a temperature sensor. Theflexible line(s) may be secured in a grid pattern on a mat for ease ofdeployment and transport, or merely connected to one another and placeddirectly on a surface beneath a container. The flexible lines may becommercially available fabric-covered, flexible fire hoses, typicallyhaving a core formed of resilient elastomeric material surrounded by afiber jacket made of polyester or similar materials.

In an alternative embodiment of this invention, the deflection membercomprises a number of discrete pressure pads arranged in a grid patternand connected to one another by substantially inflexible hoses or otherconduits. Each pressure pad, and the non-flexible hoses connecting them,is filled with a fluid. The cross sectional area of the pressure padsdecreases under the application of a load which results in an overallincrease in pressure within the grid pattern, as sensed by a pressuremeasurement device connected thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation and advantages of the presently preferredembodiment of this invention will become further apparent uponconsideration of the following description, taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is schematic, elevational view of a grid pattern of flexiblelines according to one embodiment of this invention supporting acollapsible, bulk fabric storage container;

FIG. 2 is a cross sectional view of a flexible line, in an unloadedcondition, having a first cross sectional area;

FIG. 3 is a cross sectional view similar to FIG. 2, except with theflexible line under load and having a second cross sectional area;

FIG. 4 is a perspective view of one embodiment of a single flexible linearranged in a grid pattern and secured to a mat wherein one end of theline is connected to a digital pressure gauge;

FIG. 5 is a perspective view of an alternative embodiment of a gridpattern comprising a number of flexible lines;

FIG. 6 is a perspective view of another embodiment of a grid patterncomprising a number of flexible lines;

FIG. 7 is a perspective view of a first group of flexible linesconnected to a first common line coupled to a digital pressure gauge,and a second group of flexible lines connected to a second common linecoupled to another digital pressure gauge;

FIG. 8 is a perspective view of an alternative embodiment of thisinvention in which a number of pressure pads arranged in a grid patternare connected to one another by substantially inflexible hoses or otherconduits;

FIG. 9 is a cross sectional view of a pressure pad depicted in FIG. 8,in an unloaded condition, having a first cross sectional area; and

FIG. 10 is a cross sectional view similar to FIG. 9, except with thepressure pad under load and having a second cross sectional area.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1-7, one embodiment of a measuring apparatus10 according to this invention is illustrated. As schematically depictedin FIG. 1, the apparatus 10 may support a collapsible, bulk fabricstorage container 14 of the type currently utilized by the armed forcesfor storing fuel, water and other liquids. The container 14 includes aninlet 16 for filling it with liquid, and one or more outlets 18 foremptying the liquid. As noted above, the container 14 may be formed of afabric material which assumes an irregular shape and size depending uponthe amount of liquid within its interior.

The apparatus 10 may be configured in a variety of grid patterns, eachof which comprises a deflection member in the form of one or moreflexible lines 20. In the presently preferred embodiment, and as bestviewed in FIGS. 2 and 3, each flexible line 20 may have the constructionof a fire hose or similar conduit with a core or inner layer 22 defininga hollow interior 24 and an outer layer 26 encircling the inner layer22. The inner layer 22 may be formed of an elastomeric material, such asthermoplastic polyurethane elastomer, or any other suitable materialthat is resistant to puncture and tearing and is capable of undergoingdeflection in response to the application of a load but then returningto its original shape. The outer layer 26 may be formed of any suitableabrasion and puncture resistant material, such as polyester. The hollowinterior 24 of the flexible line 20 is filled with a fluid, e.g. anincompressible liquid or a compressible gas such as air.

Various types of commercially available fire hoses are suitable for useas a flexible line 20 in the apparatus 10 of this invention. Fire hosesintended to transport water from a pumper to the hose nozzle may have anominal inside diameter of 38 mm to 76 mm and operate at pressures up toabout 2,760 kPa. Supply and relay hoses are typically larger indiameter, e.g. from 89 mm to 127 mm nominal inside diameter, and operateat pressures up to about 2,070 kPa. Forestry hoses are smaller, in therange of 25 mm to 38 mm nominal inside diameter, and operate atpressures up to about 3,105 kPa. It is contemplated that the flexiblelines 20 may also be constructed of the material used to fabricate thebulk container 14.

As noted above, the apparatus 10 may be configured in a number of gridpatterns. Referring to FIG. 4, a single flexible line 20 is arranged ina zig-zag grid pattern 28 and affixed to a mat 29 to maintain its shape.The mat 29 may be formed of a flexible material so that the apparatus 10as depicted in FIG. 4 may be rolled up for ease of transport. One end ofthe flexible line 20 in grid pattern 28 is closed and the other iscoupled to a pressure measurement device 30. One suitable pressuremeasurement device 30 may be a digital pressure gauge. Additionally, atemperature sensor 31 may be connected to the flexible line 20. Both thepressure measurement device 30 and the temperature sensor 31 may beconnected to a display 32, described more fully below in connection witha discussion of the operation of apparatus 10.

The embodiment of apparatus 10 shown in FIG. 7 employs a grid pattern 34comprising a number of first flexible lines 20′ each connected to afirst common line 36, and a number of second flexible lines 20″ eachconnected to a second common line 38. One end of the common line 36 isclosed and the other end is connected to a pressure measurement device30′. Similarly, one end of the common line 38 is closed and the otherend is connected to a pressure measurement device 30″. Each of thepressure measurement devices 30′ and 30″ 38 is connected to a display32, which also connects to a temperature sensor (not shown) as in FIG.4.

The embodiment of this invention illustrated in FIG. 5 depicts analternative grid pattern 40, and FIG. 6 shows still another grid pattern42 which also appears in FIG. 1. The grid patterns 40, 42 of theseembodiments each comprise a number of flexible lines 20 arranged inparallel columns (FIG. 5), or intersecting columns and rows (FIG. 6).The hollow interiors 24 of some or all of the flexible lines 20 in suchgrid patterns 40, 42 may communicate with one another and connect to oneor more pressure measurement devices 30 and a temperature sensor 31 (notshown in FIGS. 5 and 6).

The operation of the measuring apparatus 10 illustrated in FIGS. 1-7 ofthis invention is predicated on the concept that changes in the crosssectional area of the flexible line(s) 20 in response to the applicationof a load create changes in the pressure of the fluid within the hollowinterior 24 thereof which may be sensed by the pressure measurementdevices 30, 30′ and 30″. As schematically depicted in FIG. 2, a flexibleline 20 having a generally circular shape when unloaded may assume agenerally oval shape under the application of a load represented byarrow 44 in FIG. 3. The cross sectional area of the circular-shapedflexible line 20 in FIG. 2 is greater than that of the oval-shapedflexible line 20 in FIG. 3, although both have the same perimeterdimension. As the cross sectional area of flexible line 20 decreases,the pressure of the fluid within its hollow interior 24 increases. Thisincrease in pressure is conceptually based on the ideal gas law, PV=nRT,where P is the absolute pressure of the gas, V is the volume of the gas,n is the amount of substance in the gas, R is the gas constant and T isthe absolute temperature. According to the ideal gas law, if temperatureT is held constant, a decrease in volume results in an increase inpressure. As a practical matter, temperature of the fluid within theflexible line(s) 20 varies according to the weather conditions in whichthe container 14 is located. Consequently, a temperature sensor 31 isprovided with each of the grid patterns 28, 34, 40 and 42 describedabove to compensate for the pressure change of the fluid within theflexible line(s) 20 due to changes in temperature.

It is contemplated that a number of different means may be employed tocorrelate the fluid pressure within the hollow interior 24 of flexiblelines 20 with the mass of liquid within the container 14. One method ofcorrelating fluid pressure to liquid mass may be to calibrate aparticular grid pattern 28, 34, 40 or 42 at different temperatureswithin a range of average temperature for the area in which theapparatus 10 may be used. The calibration procedure may proceed asfollows. Assuming a container 14 to be used with the apparatus 10 has aknown mass when empty and a known mass when full of a particular liquid,e.g. fuel, water etc., readings from the pressure measurement device(s)30, 30′ or 30″ coupled to the flexible tube(s) 20 of such grid patterns28, 34, 40 or 42 may be obtained from the application of weights theretoequal to the mass of the container 14 when it is empty, equal to themass of the container 14 when it is full of liquid, and, equal to themass of the container 14 at each of a desired number of increments inbetween empty and full. In this manner, each reading obtained from thepressure measurement device 30 may be calibrated to a known mass appliedto the flexible line(s) 20 in a particular grid pattern 28, 34, 40 or42, at a known temperature.

For purposes of illustration, an empty container 14 placed on a flexibleline 20 within a grid pattern 28, 34, 40 or 42 may result in nodeflection or reduction in cross sectional area of such line 20, asshown in FIG. 2, but when filled the container 14 may cause the flexibleline 20 to reduce in cross sectional area as depicted in FIG. 3. As thecontainer 14 is emptied from a filled condition, the cross sectionalarea of the flexible line 20 increases from that shown in FIG. 3 to thatillustrated in FIG. 2. The pressure of the fluid within the hollowinterior 24 of the flexible tube 20, in turn, corresponds to its crosssectional area between the unloaded and fully loaded extremes depictedin FIGS. 2 and 3. The different pressure readings provided by thepressure measurement devices 30, 30′ and 30″ may be correlated to thevalues obtained during the calibration process described above toprovide an accurate indication of the mass of the liquid in thecontainer 14 at any point between empty and full for a giventemperature. The pressure measurement device 30 and the temperaturesensor 31 may be connected to a display 32 having a processor or othermemory device. The display 32 may compare the reading or signal receivedfrom the pressure measurement device 30 and the reading or signal fromthe temperature sensor 31, to the data obtained from the calibrationprocedure described above and provide a digital display of the mass ofthe liquid within the container 14 corresponding to the sensed pressureat a sensed temperature.

Alternatively, it is contemplated that an algorithm may be employed todirectly convert readings from the pressure measurement devices 30, 30′and 30″ to a digital display of the mass of liquid within a container14, accounting for the temperature of the fluid within the line(s) 20 inthe area the container 14 is located as sensed by the temperature sensor31. The algorithm may be contained within a processor associated withthe display 32.

Referring now to FIGS. 8-10, an alternative embodiment of a measuringapparatus 50 according to this invention is illustrated. The apparatus50 comprises a number of discrete pressure pads 52 arranged in a gridpattern 54 and connected by lines 56 which are substantially inflexibleunder the application of a load applied by the container 14 whencompletely filled. The pressure pads 52 are preferably generallydisc-shaped, although other shapes may be utilized, with a core or innerlayer 58 defining a hollow interior 60 and an outer layer 62 encirclingthe inner layer 58. The hollow interior 60 of pressure pads 52 and lines56 are filled within a fluid such as a liquid or air. Such layers 58 and62 may be formed of the same materials as the flexible line(s) 20described above in connection with a discussion of FIGS. 1-7.

The pressure pads 52 behave in essentially the same fashion as flexibleline(s) 20 under the application of a load. A pressure pad 52 having thecross-sectional shape depicted in FIG. 9 when unloaded may assume theshape illustrated in FIG. 10 under the application of a load representedby arrow 64 in FIG. 10. The cross sectional area of the pressure pad 52in FIG. 9 is greater than that of the pressure pad 52 in FIG. 10,although both have the same perimeter dimension. As the cross sectionalarea of pressure pad 52 decreases, the pressure of the fluid within itshollow interior 60 increases. The pressure within the grid pattern 54may be sensed by a pressure measurement device 30, and the temperatureof the fluid within the pressure pads 52 and lines 56 may be determinedby a temperature sensor 31. Both the pressure measurement device 30 andthe temperature sensor 31 are preferably coupled to a display 32.Further, the measuring apparatus 50 is calibrated, and operates in thesame fashion, as the measuring apparatus 10 described above.

Among the advantages of the measuring apparatus 10 and the measuringapparatus 50 of this invention is that they are capable of providingaccurate readings of the mass of liquid within a container 14 that isflexible and varies in size and dimension as it transitions between anempty and filled state. So long as the overall dimension of the gridpatterns 28, 34, 40, 42 and 54 are at least equal to the dimension ofthe container 14 when full, a decrease in the size of the container 14does not affect the pressure measurements needed to obtain an indicationof the mass of liquid within the container 14, as described above. Thecontainer 14 may even extend in between adjacent flexible lines 20within a grid pattern 28, 34, 40 or 42, or between pressure pads 52within the grid pattern 54, and touch the surface beneath, withoutimpairing the accuracy of pressure readings. Further, the measuringapparatus 10 and the measuring apparatus 50 are light weight, portableand relatively inexpensive to manufacture or repair.

While the invention has been described with reference to a preferredembodiment, it should be understood by those skilled in the art thatvarious changes may be made and equivalents substituted for elementsthereof without departing from the scope of the invention. In addition,many modifications may be made to adapt a particular situation ormaterial to the teachings of the invention without departing from theessential scope thereof.

For example, while only the grid pattern 28 depicted in FIG. 4 isillustrated with a mat 29 connected to a flexible line 20 it iscontemplated that any or all of the other grid patterns 34, 40, 42 and54 could employ a mat 29. Further, the grid patterns 28, 34, 40, 42 and54 are depicted for purposes of illustration only and other arrangementsof one or more flexible lines 20, or pressure pads 52, in different gridpatterns are considered within the scope of this invention.

Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

1. Apparatus for measuring the mass of a liquid, comprising: a bulkfabric storage container having an expanded size when filled with theliquid and a smaller, collapsed size when empty; at least one deflectionmember arranged in a grid pattern upon which said bulk fabric storagecontainer is positioned, said grid pattern having a size at least equalto said expanded size of said bulk fabric storage container, said atleast one deflection member having a hollow interior filled with afluid, said at least one deflection member being movable between a firstposition in which said hollow interior has a first cross sectional areaand said bulk fabric storage container is empty, and a second positionin which said hollow interior has a second cross sectional area and saidbulk fabric storage container is full, said second cross sectional areabeing less than said first cross sectional area, said at least onedeflection member being effective to assume any cross sectional areabetween said first and second cross sectional areas in response tovariations in the mass of the liquid within said bulk fabric storagecontainer; at least one pressure measurement device coupled to said atleast one deflection member, said at least one pressure measurementdevice being effective to sense the pressure of said fluid within saidhollow interior of said at least one deflection member with said bulkfabric storage container resting on said grid pattern and while the sizeof said bulk fabric storage container varies between said expanded sizeand said collapsed size as liquid is introduced into or removed fromsaid bulk fabric storage container, the pressure sensed by said at leastone pressure measurement device varying in relation to said crosssectional area of said at least one deflection member, said at least onepressure measurement device producing a measurement of said pressurethat may be correlated to the mass of the liquid within said bulk fabricstorage container.
 2. The measuring apparatus of claim 1 in which saidat least one deflection member comprises at least one flexible line. 3.The measuring apparatus of claim 2 in which said at least one flexibleline comprises a number of flexible lines each having a hollow interiorwhich communicate with one another.
 4. The measuring apparatus of claim2 in which said at last one flexible line is a fabric-covered flexiblehose.
 5. The measuring apparatus of claim 2 in which said at least oneflexible line arranged in a grid pattern is affixed to a mat.
 6. Themeasuring apparatus of claim 1 further including a temperature sensorcoupled to said at least one deflection member, said temperature sensorbeing effective to sense the temperature of the fluid within said hollowinterior of said at least one deflection member.
 7. A method ofmeasuring the mass of a liquid, comprising: (a) providing a bulk fabricstorage container having an expanded size when filled with the liquidand a smaller, collapsed size when empty; (b) providing at least onedeflection member arranged in a grid pattern having a size at leastequal to said expanded size of said bulk fabric storage container, saidat least one deflection member having a hollow interior filled with afluid; (c) placing the bulk fabric storage container onto said gridpattern of said at least one deflection member, said at least onedeflection member being movable from between a first position in whichsaid hollow interior has a first cross sectional area and wherein saidbulk fabric storage container is filled with liquid, and a secondposition in which said hollow interior has a second cross sectional areaand wherein said bulk fabric storage container is empty; (d) sensing thepressure of the fluid within said hollow interior of said at least onedeflection member while said bulk fabric storage container varies insize between said expanded size and said collapsed size as liquid isintroduced into or removed from said bulk fabric storage container, saidpressure varying in relation to said cross sectional area of said hollowinterior of said at least one deflection member; (e) correlating thepressure sensed in step (d) to the mass of the liquid within said bulkfabric storage container.
 8. The method of claim 7 in which step (b)comprises providing at least one flexible line having a hollow interior.9. The method of claim 7 further including: (f) sensing the temperatureof the fluid within said hollow interior of said at least one deflectionmember; (g) adjusting the magnitude of the pressure sensed in step (d)in relation to the temperature sensed in step (f); and (h) correlatingthe magnitude of the pressure as adjusted in step (g) to the mass of theliquid within the bulk container.